Remote control for radio apparatus



Jan. 26, 1937. G. BEERS 2,059,127

REMOTE CONTROL FOR RADIO APPARATUS Filed April 25, 1933 2 Sheets-Sheet l.

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REMOTE CONTROL FOR RADIO APPARATUS Filed April 25, 1935 2 Sheets-Sheet 2 Patented Jan. 26, 193'? PATENT OFFIQE George L. Beers, Collingswcod, N. 5., assignor to Radio Corporation of America, a corporation of Delaware Application April 25, 1933, Serial No. 667,774

8 Claims.

The present invention relates to radio receiv ers and more particularly to control systems therefor.

One of the main objections to known remote control systems for radio receivers isthat the added cost which is entailed thereby is often excessive and prohibitive to commercial use of such systems. Accordingly, it is an object of my'invention to provide a remote control system for a radio receiver, which does not add greatly to the cost of the receiver.

Another object of my invention is to provide an improved receiver which permits remote control of tuning and other functions of the same without added complication and excessive cost characteristic of known receiving systems and receivers embodying such control.

More specifically, an object of my invention is to provide a superheterodyne receiver so designed that a portion of the superheterodyne circuit and associated apparatus forms a remote control unit which may be utilized as a unitary part of the receiver, or which alternatively, may be connected as a remote control unit, to the main unit of the receiver by a cable.

A further object of my invention is to provide a receiver of the above-mentioned character in which the remote control unit may be combined with the main receiver unit to form a receiver of conventional appearance to be operated in the conventional manner.

A still further object of my invention is to provide a remote controlunit of the above-mentioned type, in which a minimum number of conductors are required in the remote control cable to effect a desired high degree of control and efiicient operation of the receiver.

Other features and advantages of my invention will appear from the following description when taken in connection with the accompanying drawings, in which Figure l is a circuit diagram of a radio receiver embodying my invention;

Fig. 2 is a front View of my radio receiver showing the remote control unit positioned within the main unit to form a conventional receiver;

Fig. 3 is a perspective view showing the receiver arranged for remote control, the two receiver units being connected by a cable;

Fig. 4 is a plan view, partly in section, of the receiver of Fig. 1 showing how the remote control unit and the main unit are connected by a cable; and

Fig. 5 is a plan view similar to Fig. 4 illustratingamodified form of my invention.

(Cl. 250Z) Referring to Fig. 1, the embodiment of the invention illustrated comprises a superheterodyne receiver which is divided into two portions, a remote control portion It) which is shown enclosed in the dotted rectangle H, and a main receiver portion l2 which is shown enclosed in the dotted rectangle I3. These two portions of the receiver are connected by a cable M.

The remote control unit Ill includes a radio frequency amplifier tube l and another tube It which functions both as an oscillator and the first detector. The main receiver unit 12 includes intermediate frequency amplifier tubes l7 and iii, an automatic volume control tube IS, a second detector, indicated at 20, an audio amplifier indicated at 2i, and a power supply unit indicated at 22.

Considering the circuit in detail, an antenna or signal source 23 is connected to the primary 24 of a shielded transformer 28 located in the main receiver unit l2. The secondary 21 of the transformer 26 is coupled to the primary 28 of a radiofrequency transformer 29 in the remote control unit It by means of a coupling condenser 30 and a cable lead 3!. The radio frequency connection through the primary winding 28 is completed through a condenser 32 which connects the lower end of winding 28 to ground.

The secondary 33 of the radio frequency transformer 29 is shunted by a variable condenser 34 and a by-pass condenser 36 in series. The condenser 34 tunes the secondary circuit to the desired radio frequency, the capacity of condenser 36 being so large that it has but little effeet on the tuning.

The radio frequency amplifier tube [5 is preferably of the screen-grid type and comprises a heater 3?, an indirectly heated cathode 33, a control grid 39, a screen grid 40, a suppressor grid 4!, and an anode 42. The suppressor grid is mainly for the purpose of preventing secondary-emission from the anode.

The tunable secondary circuit of the radio frequency transformer 29 is connected to the control grid 39 through a lead 43. It is connected to the cathode 38 through ground and through a biasing resistor 54 shunted by a condenser 46, this resistor with its variable tap t? forming a sensitivity control for the receiver, as well as supplying the proper grid bias.

A biasing potential is supplied to the control grid 39 over the same cable conductor 3| to which the antenna 23 is coupled. This grid biasing connection may be traced from the biasing resistor 48 in the automatic volume control circuit, through the conductor 49, the high resistance unit 50, through the conductor cable 3 I, the primary winding 28, the resistor 5!, and through the secondary winding 53 to the control grid 39. The biasing resistor 46 is shunted by a condenser of the proper capacity to give the resistance and capacity combination a time constant such that audio frequencies will not be impressed on the grids of the tubes which are biased for automatic volume control by the resistor 36.

The resistor 5i which has a value of the order of 500,000 ohms, and the condensers 32 and 36 form a filter which filters the hum induced in the lead 3I by the filament heater current to keep it from being impressed on the grid of tube I5.

The vacuum tube I6 includes the grid and plate elements of both an oscillator and a first detector, these elements having a common cathode 52 and heater element 53. The oscillator elements consist of the control grid 54 and the grid or plate element 55.

The first detector elements consist of the control grid 56, the screen grids 51, and the plate 58.

The output of the radio frequency amplifier i5 is coupled to the first detector through a radio frequency transformer 59 which has its secondary 69 tuned by a variable condenser 6|. A certain amount of capacity coupling is provided by means of an open-ended winding 62.

The tuned secondary winding 69 is connected to the control grid 56 through a lead 63. It is connected to the cathode 52 through ground and through a biasing resistor 64 which is shunted by a by-pass condenser 66.

The screen grids 49 and 51 of the tubes I5 and it are supplied with a positive direct-current potential by the power supply unit 22 through a circuit which may be traced from the power supply resistor 61 through the lead 68, the cable conductor 69, the conductor 65, the resistor I0, the lead 1! to the screen grids 51, and the conductors I2 and I3 to the screen grid 40.

The plate 42 of tube I5 is connected to the plate supply conductor 65 through the primary winding of the transformer 59, while the plate 53 of the tube I 6 is connected to the conductor 65 through an inductance coil IA.

The heaters 31 and 53 of the tubes I5 and I6, respectively, are connected in series and supplied with current by a transformer I6 connected to the alternating-current line. The heater circuit may be traced from the secondary winding of transformer I6 through the conductor III, the cable conductor I8, the filament 37, the filament 53, to ground. In order to keep heater current through the cable conductor I8 at a low value, the tubes have 6 volt heater filaments. The tubes in the main section of the receiver have 2.5 volt alternating current heater filaments connected in parallel.

The oscillator is of the type which has a plate coil I9 coupled to a tuned grid coil 80, the plate 55 being connected to the high potential lead 65 through the plate coil I9. The control grid 54 is connected through a lead 8I to the grid coil 89 which is tuned by a variable condenser 82 and a fixed condenser 83 connected in series and shunted across the coil. The junction point of the condensers 82 and 83 is connected directly to ground, while the lower end of the coil 89 is connected to ground through a grid-leak resistor 84. The variable condenser 82 is employed to vary the frequency of the oscillator.

The oscillator is coupled to the first detector by virtue of the fact that the electrodes of the oscillator and first detector are in the same electronic stream.

The intermediate frequency amplifier tube I! is of the screen grid type having a heater element 55, a cathode 81, a control grid 88, a screen grid 89, a suppressor grid 90, and an anode 9I. The control grid 58 is negatively biased by means of a connection through the grid resistor 92 and the conductor 93 to the grid biasing resistor 48 in the volume control circuit, and also by means of resistor I95 in the cathode circuit.

The input circuit of the intermediate frequency amplifier I7, which is tuned to the intermediate frequency output of the first detector, comprises an inductance coil 94 shunted by two condensers 96 and 91 connected in series. The upper terminal of the inductance coil 94 is connected to the control grid 88 of the amplifier tube I1 through a condenser 98. The lower terminal of the inductance coilhas a low impedance radiofrequency connection to the cathode 8? through a circuit which may be traced through the conductor 99, the cable conductor 69, the conductor 65, the condenser I99, and through ground and the by-pass condenser IflI (shunting biasing resistor I65) back to the cathode 87.

The output circuit of the first detector'is coupled to the input of the intermediate frequency amplifier l'I through two circuits tuned to the intermediate frequency and coupled by a condenser 91, common to the two circuits. The first tuned circuit may be traced from the plate 58 of the first detector tube, through a tuning condenser I02, the lead I93, the cable conductor I94, the connection I 09, through the condenser 91, through the connection 99, the cable conductor 69 and the conductor 65 to the lower end of the inductance coil l hand through coil I4 back to condenser I92. It will be noted that the cable conductor 69 serves both as a coupling conductor for the intermediate-frequency circuit and as a plate supply lead for the tubes I5 and I6.

The second tuned circuit is the one comprising inductance coil 94 and condensers 96 and 91.

It will beapparent that the capacity between the cable conductors I94 and 69 is in shunt to the condenser 9'I,and will have some efiect upon the tuning of the circuits. It is desirable to make this effect negligible because it is diflicult to obtain cables having uniform capacity between conductors, and also because it may be desired to use various cable lengths. This is accomplished both by using the specific type of coupling described above and by making the capacity of condenser 97 very large compared with the capacity between conductors I94 and 69.

For example, in an embodiment of my invention, using an intermediate frequency of kilocycles, the following values may be employed: condenser 97-5000 micro-microfarads; condenser 96-175 micro-microfarads; condenser .102-175 micro-microfarads; capacity between conductors 104 and (iii-approximately 400 micro-microfarads.

The above-described scheme for coupling the output circuit of the first detector to the input circuit of the intermediate amplifier was employed after various coupling circuits had been tried without success. For example, it was found that inductive coupling could not be employed because the cable capacity Was in shunt to the coupling coil and formed a resonant circuit therewith. This resonant circuit introduced an undesired peak in the selectivity curve of the coupling circuit, and, in general, made it impossible to give the coupling circuit the proper selectivity characteristics. No such difiiculty is encountered when using the coupling circuit shown in Fig. 1, since there is no third resonant circuit. By employing such a coupling circuit, the two tuned circuits can be given critical coupling and the desired fiat-topped selectivity curve obtained.

The plate SI of the intermediate frequency amplifier tube is connected to the resistor 61 of the power supply unit through a conductor I01, the primary I08 of a tuned intermediate-frequency transformer, and a conductor I09. The secondary H of the tuned transformer is connected to the input circuit of the second detector 20. The output of the second detector 20 is supplied to the audio amplifier 2I through an audio transformer III, and from the audio amplifier 2I to a loudspeaker I I2 through an output transformer I I3.

Manual volume control is provided at the remote control unit I0 by means of a potentiometer II4 which is shunted across the output of the second detector 20 through cable conductors Ill and I I8. The upper terminal of the primary of the audio frequency transformer I II is connected to a variable tap H6 on this potentiometer through cable conductor II5.

Automatic volume control is provided by means of tubes I8 and I9, tube I8 being a screen grid tube having a heater element I I9, a cathode I20, a control grid I2 I, a screen grid I22, a suppressor grid I23, and an anode I24, and tube I9 being a rectifier tube comprising a heater element I26, a cathode I21, and an anode I28.

The control grid I2I of tube I8 is connected, through a coupling capacity I29, to the upper terminal of the inductance coil 94 in the tuned intermediate frequency circuit. It is biased through high resistance I30 and a biasing resistor I3I which is shunted by a by-pass condenser I32. The screen grid I22 of the volume control tube I8, as well as the screen grid 89 of the intermediate frequency amplifier tube IT, is connected to the resistor 61 of the power supply unit through a conductor I33. The plate I24 of tube I8 is connected to the power supply resistor 61 through the primary I34 of a transformer I35, which feeds the output of tube I 8 to rectifier tube I9.

The upper terminal of the secondary I36 of this transformer is connected to the plate I28 of the rectifier tube I9. The lower terminal of the secondary I36 is connected through a biasing resistor 48 to ground, and from ground through the lower section I31 of the power supply resistor 61 and through a conductor I38 to the cathode I21 of the rectifier tube.

The lowersection I3! of the resistor 61 is included in series with the biasing resistor 48 in order to give a delayed volume control action.

,Referring to Figs. 2 and 3, the portion of the apparatus shown enclosed in rectangle I3 in Fig. 1 is mounted in the cabinet I40, the loudspeaker II2 being mounted in the lower part behind a grille MI. The upper part of the cabinet has a panel I42 in the front thereof, which may be concealed by means of two doors I43.

The panel I42 has an opening or recess therein for the reception of the remote control unit I0 which is mounted in a small cabinet I44 having a front panel I46 carrying part of the receiver controls. These controls are the sensitivity control I41 (tap 41 in Fig. 1), the tuning control I48 (connected to the three ganged condensers) mounted underneath the tuning dial I45, and the volume control I49 (tap I I6 in Fig. 1).

Two controls are mounted on the panel I42 of the main cabinet, these being a tone control knob I50 for low frequency response, and a tone control knob II for high frequency response.

As shown in Fig. 2, the remote control unit I0 may be placed in the opening in the panel of the main unit, with the panel I46 of the remote control unit flush with the panel I42 of the main unit to form a receiver of substantially conventional appearance. Or, if desired, the remote control unit I0 may be pulled out of the main cabinet and placed on a stand and the two units connected together by means of the cable I4 as indicated in Figs. 3 and 4, so that the main unit of the radio receiver may be operated from a remote point.

As shown in Fig. 4, there is preferably a plug I53 mounted on the back of the remote-control unit I0 and a plug socket I54 so mounted on the main receiver unit I2 that, when the remotecontrol unit is moved into position in the panel opening, the plug I53 and. socket I54 engage automatically. In the specific arrangement illustrated in Fig. 2, the cable I4 can be plugged into the socket I54 at the rear, while the remote-control unit is plugged in at the front. For remote control, the remote-control unit I0 is pulled out of the opening and plugged into the cable socket I55.

As shown in Fig. 3, a door I56, hinged at its upper edge, may be mounted inside the opening of the panel I42 and so arranged that when the remote control unit In is removed, the door will drop down by gravity or spring action to close the panel opening. If such a door is provided, it may be desirable to omit the doors I 43.

Instead of using an arrangement in which the cable I4 is plugged into the back of the remote control unit when the remote control feature of the receiver is to be utilized, it may be desirable to employ the arrangement shown in Fig. 5. In this arrangement the cable I4 is permanently connected to the remote control unit I0 and is wound up on a reel I5! which operates the same as a window shade roller. A cable pig-tail connection I58 is provided between the reel and the receiver circuit.

Obviously, the location of the recess for the remote control unit is not restricted to the front panel of the main unit. It may be in the top of the main unit or it may be at the upper front edge of the large cabinet in the form of a notch in the cabinet edge.

Various other modifications may be made in my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and are set forth in the appended claims.

I claim as my invention:

1. In a radio receiver circuit, a radio frequency transformer having a primary winding and a secondary Winding, an electric discharge device having input electrodes connected to said secondary winding, a source of signals connected to said primary winding, a high impedance unit, said secondary Winding being connected at one terminal end only through said high impedance unit to one terminal end only of said primary winding, said terminal ends being above ground at a direct current potential, and a common circuit lead for transmitting both a signal current from said source and a biasing potential through said primary winding connected to the opposite terminal end of the primary winding.

2. A superheterodyne receiver comprising a remote-control section and a main section, said remote-control section including a radio frequency amplifier tube, an oscillator, and a first detector, said main section including an intermediate frequency amplifier and a second detector, a cable including a plurality of conductors for electrically connecting said two sections, a source of biasing potential in said main section, a radio-frequency transformer having a secondary connected between the control grid and cathod of said radiofrequency amplifier tube, the connection to said grid being conductive, and a conductive connection between said source of biasing potential and said secondary whereby said grid is biased, said connection including one of said cable conductors, an antenna coupled to a point on said last-named conductive connection at said main section, and a high impedance connected in series with said conductor between said source of biasing potential and said point.

3. In a radio receiver, a main unit including at least a portion of a tuned circuit comprising an inductor and a capacitor, a remote control unit including at least a portion of a second tuned circuit comprising an inductor and a capacitor, and means for transferring signal energy from one of said units to the other of said units, said means comprising two adjacent conductors which have substantial capacity between them and a coupling capacitor which is connected in series with said first inductor and said first capacitor to complete said first tuned circuit and which is also connected in series with said second inductor and said second capacitor to complete said second tuned circuit, said coupling capacitor also being in parallel with the capacity between said conductors and being of a value to provide critical coupling between said tuned circuits.

4. A radio receiver having a portion of the elec trical units installed in a cabinet and having another portion of the electrical units installed in a portable remote-control box, said other portion including the tuning elements of the receiver, and means for electrically coupling said two por tions, said means comprising two coupled circuits, each including reactance units and both tuned to the same frequency and at least one of them including two parallel conductors which have capacity between them, the means for coupling said two tuned circuits comprising a reactance common to said tuned circuits, said common reactance being connected in series with the reactance units of each tuned circuit and consisting of the capacity between said conductors and a condenser having a substantially larger capacity than the capacity between said conductors.

5. A radio receiver comprising a main unit and a remote-control unit, said remote-control unit including means for converting a radio frequency signal to an intermediate frequency signal, said main unit including means for converting said intermediate frequency signal to an audio fre quency signal, and coupling means for transferring the intermediate frequency output of said signal to an intermediate'frequency signal, said main unit including means for converting said intermediate frequency signal to an audio frequency signal, and means for transferring said intermediate frequency signal from said remotecontrol unit to said main unit, said means comprising two coupled circuits, each of said' circuits being tuned to said intermediate frequency and including two parallel conductors which have substantial capacity between them, the means for coupling said two tuned circuits comprising a reactance common to said tuned circuits, said reactance consisting of the capacity between said conductors and a condenser having a substantially larger capacity than the capacity between said conductors, said common reactance being serially connected in each of said tuned circuits.

'7. A radio receiver comprising a main unit and a remote-control unit, said remote-control unit including means for converting a radio frequency signal to an intermediate frequency signal, said main unit including means for converting said intermediate frequency signal to an audio frequency signal, and means for transferring the intermediate frequency output of said remote-control unit to the intermediate frequency input circuit of said main unit, said transferring means comprising two capacity-coupled tuned circuits which include cable conductors, one of said tuned circuits being completely contained in one of said units, except for the capacity between said conductors, and the other of said tuned circuits including at least one reactance element located in the other of said units and also including said cable conductors, the capacity which couples said tuned circuits being serially connected in each of said circuits.

8. Radio apparatus comprising a main unit and a remote-control unit, a cable including a plurality of conductors for electricallyconnecting said units, one of said units including an in ductance coil shunted by two condensers connected in series and tuned by said two condensers to a certain frequency, the other of said units including a tuning coil, one terminal of said tuning coil being connected to the junction point of said two condensers through a tuning condenser and one of the conductors of said cable, the other terminal of said tuning coil being connected to the other terminal of one of said two condensers by means of another of the conductors of said cable, the capacity of said one condenser being several times as great as the capacity between said twocable conductors, said tuning coil, said tuning condenser, and said one condenser forming another resonant circuit tuned to said certain frequency.

GEORGE L. BEERS. 

